(1) Field of the Invention
The invention relates to a method and apparatus for the on-line determination of laminate bond strength by a nondestructive, noncontact method.
(2) Description of the Prior Art
Measuring the bonding strength of a plural layered laminate whether prepared utilizing an adhesive material or whether prepared by heat sealing a thermoplastic layer of the laminate to a second laminate layer has up until now been accomplished by a tedious, time consuming destructive method involving peeling the laminate apart and measuring the force required to delaminate the assembly. Such assemblies as plastic, wood, and fabric laminates are often utilized. The quality of such laminates can vary depending upon the strength of the adhesive bond. It would be desirable to obtain an indication of the strength of the adhesive bond during the preparation of the laminate on high speed lamination equipment. Great savings could be made if the bond strength could be determined on-line prior to the preparation of large amounts of defective laminate.
The on-line monitoring of the specific surface of mechanical pulps by measuring the light scattering characteristics of the pulp sample is disclosed in U.S. Pat. No. 4,441,960. The on-line measurement of inclusions in pulp slurries is disclosed in U.S. Pat. No. 4,402,604. In this method an apparatus for measuring inclusions comprises a series of photosensitive devices arranged to receive light reflected from or transmitted through the pulp material.
In U.S. Pat. No. 3,574,470 there is disclosed a method and device for detecting abnormal voids in a low density material such as polyurethane foam by measuring the light reflected from the foam; the intensity of the reflected light decreasing when the incident light is beamed into a low density material having an abnormal void. In U.S. Pat. No. 4,215,939, a method and apparatus is disclosed for measuring the presence of a glue drop on the reflective inner surface of a closure by directing collimated light onto the closure and measuring the amount of light remaining collimated after reflection from the closure.
Other methods of measuring the bond strength of an adhesive material utilized to bond layers of a laminate are disclosed in U.S. Pat. No. 3,770,547 and U.S. 3,740,290 wherein a method is disclosed to provide for development of a color in the adhesive to indicate sufficient reactivity of the adhesive. In U.S. Pat. No. 4,232,559 a means is disclosed for determining the area of contact of an adhesive material with a substrate by comparing the amount of light reflected through the right angle sides of a prism when the hypotenuse face of the prism is in contact with the adhesive as compared to when the hypotenuse face is not in contact with the adhesive; the adhesive having an index of refraction higher than that of the prism.